Floor grates are a major SAFETY HAZARD! - They can contribute to the spread of fire and even more of a problem is that if you have a CO leak, they allow the easy passage of gas into the sleeping areas. You would be best off to restore the integrity of your floors, and find some other means of distributing the heat, but if you aren't willing to do that, PLEASE make sure that you have a goodly number of CO and smoke detectors installed, and that you have tested them for proper operation.
Gooserider
Gooserider
